Telephone system



Feb. l2, 1929.

A. J. RAY ET AL 'TELEPHONE-SYSTEM original Filed 4Feb. l22, 1925 @55 saqwuvw 7% A m Nl \do W mlm@ Q Mv mi, wv v MWIIIIIII FQQQ* Mw uw b NN o EnU-En Drs J. Fag,

Hhur

Patented Fels. l2, 19239.

narran rieur oFFIcE.

ARTHUR J. RAY, OF CUBA, AND RUDOLPH F. TEHLIK, 0F CHGAGO, LLINOIS, AS-

SIGNORS, BY MESNE ASSIGNMELVTS, TO AUTOMTICELECTRIC INC., OF CHICAGO,ILLENOIS, A CORPORATION OF DELAVARE, Y

rnnnrnonn SYSTEM.

Application filed February 2, 1925, Serial No. 6,181. Renewed July 5,1928.

The present invention relates in genera to telephone systems, hut isconcerned more particularly with telephone systems in which ar--rangements are provided for absorbing' one or more digits in certain ofthe telephone numbers, and is concerned still more particularly withtelephone systems in which the absorbing arrangement comprises asocalled drop-haelt7 selector-i. e., a selector which responds to adigit and then restores to its normal position after which it respondsto the nent digit dialled and selects an idle trunk in the desired levelafter the fashion ot any ordinary selector.

@ne feature of the present invention is the provision ot' a new andimproved circuitar rangement in a` discriminating drop-hack selectorwhich is required to drop hack from a majority of its levels, but nottrom the others. Jfrccording` to thisteature, the selector is providedwith circuit arrangements which normally cause the selector to drop hackin response to any first digit, in conjunction with vcontacts operatedin Vaccordance with the extent ot the tlrst'movement ot the switch inresponse to such lirstdigit to prevent the dropping hack o'f theselector on a certain level, or certain levels, as the case may loe. I y

There isanother feature of this invention which consists in a new andimproved circuit arrangement. for preventing,` the automatic rotarymovement trom taking place on levels trom which it is desired to drophack, and this ar" igjement consists in the provision oi s -controlledcontacts for opening;v the circuit ot the rotary magnet when the shaftis raised to a level from which the drop hack is to he made, inconjunction with, contacts on the release magnet i'or maintaining; thecircuit ot the rotary magnet open until the shart reaches its normalposition.

flnother feature ot1 this case relates to the provision of a new andimproved arrangement tor insuring` that the relay which operates inseries with the release magnet when the normal position is reached bythe shaft ot the selector after it has dropped hack to alosoro a digitdoes not pull up and open its -fore it is fully released.

Another feature of this case which may he considered as more or lessdependent upon the preceding` one, is concerned with the provision otcircuit arrangements whereby the switching relay o'tl the switch isdisconnected from the release trunk conductor during] the releasingoperation to prevent its energization which would otherwise occurresponsive to the grounding ot the release trunk conductor.

Referring now to the accompanying drawings, Fig. l shows a trunlringlayoutillustratingl one situation in which the new and improveddrop-back selector may he used to an advantage, and 2 is a circuitdrawing,` ot a drop-back selector embodying the features oit' theinvention.

Referring,` now particularly to Fig. l, this drawing' shows the selectorD which is located in an oiiice' of a multi-oliice network embracing notmore than ten automatic otlices ot an ultimatecagacity of 10,000 lineseach. t'is assumed, however, that at pres; ent only the #toiiice has`more than one thousand lines assigned and that the other oiiiees areaccordingly of one thousand lines capacity or less. That being the case,thousands selectors are required in the #al oiicc but not in the otheroiiices.

Trunks leading to thousands selectors in the :,/gtl ol'lice terminate inthe 'fourth level oi the selector D. One ot these thousands selectors isthe selector E. The hundreds selector F and the connc-zctory El may heused to entend a connection to the line ot' substation A2.

Trunks leadingirom the sixth level of the selector D extendtohundredsseleetors in the sixth oiiice which, at present, has acapacityet not more than 1000 lines. Gneot these trunk lines terminates in theselector F which may be used in conjunction with the connector H toextend the connection to the line of substation A.

The remaining working levels of the selector D are understood to beconnected up in a manner similar to the sixth level.

Regarding the selector D itself, it maybe pointed out that this is astandard two-wire selector of the usual vertical and rotary type withcertain eXtra equipment consisting of an added relay 2l and the shaftsprings which operate on the fourth level, together with certain othercircuit arrangements, all of which co-operate together to bring aboutthe desired action of the selector which is to release on the calling ofany digit unless it is prevented from doing so by the operation of theshaft springs, and to act like any ordinary selector upon the diallingof the next digit in case it releases in response to the dialling of thedigit in question.

The invention having been described generally, a detailed description ofthe operation of the apparatus shown will now be given. For,

this purpose, it will be assumed that the sub scriber at substation Adesires to converse with the subscriber at substation A, whose number is66461. The subscriber at substation A now removes his receiver',whereupon the individual line switch extends the calling line totheterminals (such as 2, 3, and 4) ofan idle first selector switch, whichselector, it will be assumed, is the selector D.

l/illien the selector D is seized, as above pointed out, line relay 22energizes over conductors 5 and 7 and over the calling line and closesat armature 3l a circuit for release relay 28. Release relay 23energizes and prepares the switch for operation at armatures 33 and andat armature 32 places ground on the release trunk conductor 6 so as tomaintain the line switch C operated.

lhen the calling subscriber turns his calling device in accordance withthe first digit in the desired number, in this case the digit 6, linerelay 22 deenergizes momentarily for each of the six interrnptionsproduced in its circuit by the calling device at the calling substation.Each time it deenergizes, line relay 22 closes at armature 3l a circuitthrough armature 33 and its working contact and the series relay 24 forvertical magnet 47. P the operation of vertical magnet 47, the wipers48-50 are raised step by step and they come to rest opposite the desiredlevel of bank contacts, in this case the sixth level. Relay 24 isenergized in series with vertical magnet 47 upon the first impulse ofcurrent being delivered to the latter and, being slow acting, maintainsits armature attracted throughout the series of impulses. At armature39, relay 24 disconnects the grounded release trunk conductor 6 from theoff normal contacts 37, se as to prevent the premature operation ofrelease magnet 86. At armature 40, relay 24 closes a point in thecircuit of stepping relay 25 which is complet-ed at olf normal contacts54 upon the first vertical movement of the shaft. This circuit startsfrom the grounded release trunk conductor 6 and includes armature 88 ofrelease magnet 36 and its resting contact, working contact and armature40, and. off normal contacts 54. Upon the completion of this circuit forrelay 25, relay 25 energizes and closes at armature 4l a. lockingcircuit for itself which includes the resting contact and armature ofswitching relay 26, working contact and armature 4l, and the interruptercontacts 55 of the rotary magnet 56, in addition to the off normal`contacts 54. At armature 42, relay 25 closes a point in the circuit ofrotary magnet 56.

Since the sixth level is the one called and since the shaft springs areoperated on the fourth level, these springs are momentarily operated asthe operating portion of the shaft passes by the projection on the shaftspring nearer the shaft. This, however, does not produce any effect, asmay be seen upon an examination of the circuit, because relay 24 isenergized at this time.

At the end of the ver vical movement on the switch, relay 24 falls backand closes at the normally closed contacts controlled by armature 40, apoint in the circuit of rotary magne.. This circuit is not completed atthis time, however, because the shaft contacts 9 are open. At armature39 relay 24 closes a circuit from the grounded release trunk con` ductor6, through off normal contacts 37, normally closed shaft contact 8,armature 27 of relay 2l and its resting contact, and olf normal contacts35 for release magnet 36. Responsive to the closure of this circuit,release magnet 36 pulls up and at armature 38 opens a still furtherpoint in the circuit of rotary magnet 56 so as to prevent a momentaryclosure of the rotary magnet circuit at contacts 9 as the shaft passesthe fourth level. Armature 3S of the release magnet also connects therelease trunk conductor 6 to the release magnet circuit at a pointbetween contacts 9 and armature 27, thereby preventing a momentaryopening of the re lease magnet circuit at contacts 8 as the switch shz tpasses the fourth level on its way 'to its normal position. As a furtherresult of the energzation of the release magnet, the shaft of the switchis restored to its normal position, whereupon olf normal contacts 35 and54 are opened. Contacts 54 open the circuit of relay 25 whichaccordingly falls back ind disconnects rotary magnet 56 at armature 42and opens a further point in its previously closed locking circuit atarmature 41.

@if normal contacts 35 open a point in the Cil contacts (not shown) inthat level, which are the contacts in which the line ot substation Aterminates. The usual ringer at the called substation is now actuatedover the called line by the connect-or l-l in the usual manner.

When the called subscriber removes his receiver, the ringing` current isremoved and the talking connection is completed in the usual manner,whereupon the two subscribers may converse with each other as desired.

lll/Then the conversation is terminated, the two subscribers replacetheir receivers with the result that the ground potential is removedtrom the release trunk conductor of the established connection by theconnector H and the ground is accordingly removed from release trunkconductor 52, Fig. 2. Vilhen this occurs, relays 2l and 26 of theselector D fall back. At armature 45, relay 2G closes a circuit througharmature 31 and its resting contact, armature B3 and its restingco-ntact, and ott normal contacts 'tor release magnet 36, whichthereupon energizes and restores the switch to its normal position. rlhecircuit of release magnet 36 is opened at oit normal contacts 35 whenthe normal position is attained. It will be noted that the lower windingof relay 2l is disconnected from around the ott normal contacts 85 atarmature 34 of release relay 23 at this time so as to prevent anyinterference with the releasing operation.

Considering now a call from the line ot' substation A to the line otsubstation A2, and assuming that, when the subscriber at substation Aremoves his receiver, the line switch C selects the selector D ashereinbe'fore described and that the selector D is accordingly preparedfor operation in the same manner as before. The dialling of the firstdigit fl in the desired number results in the transmission of tourimpulses to vertical magnet 47 through series relay 24 with the resultthat the wipers Lrg-50 are raised oppo-V site the fourth level ot bankcontacts. Since the otllce in which the line ot substation A2 terminatesis a fully equipped ten thousand line othce, no digit is to be adsorbedat this time. Therefore, the shaft springs are operated by the switchshattat this time to prevent the absorbing ot the oilice digit. Thecontacts 8 open a point in the circuit through which release magnet 36was previously operated to restore the switch to normal at the end ofthe iirst digit, `and the contacts 9 close a point in the circuit of therotary magnet 5G so that the rotary magnet may operate as soon as theseries relay 24C falls. back at the end of the digit. For the salte ofclarity it may be well to mention that the circuit of rotary magnet 56at this time is as follows: from ground by way of the grounded releasetrunk conductor 6, armature 3S and its resting contact, normally closedcontacts controlled by armature 40, the fourth level shaft con:

trolled contact 9, working contact and armature 42, and rotary magnet 56to battery. The operation ot the rotary magnet 56 and the subsequentoperation of the selector is the same as described hereinbe'lore, andassuming that the selector E is the one seized, this selector, togetherwith a hundreds selector (tor example, the selector F) and a connector(for example, the connector H) are operated to extend the connection tothe line of substation A responsive to the dialling et the remainingtour digits l, 8, 9, and 0.

At the end ot the ensuing conversation, the connection is released inthe usual manner.

Regarding the arrangement for maintaining the release trunk conductor 6grounded during the regular releasing operation of the selector, it willbe remembered that, when ground is removed from the release trunkconductor of the trunk upon which the wipers of the switch are standing,relay7 26 falls back and closes at armature Ll5 a circuit througharmatures 3l and 33 and otll normal contacts 35 tor release magnet 36;Also, relay 2l is unlocked and falls back in case it is operated t thistime. Release magnet 86, upon energizing responsive to the closure ofits circuit, closes at armature 38 and its front contact a point in thecircuit through which it is locked to the release trunk conductor`during the dropbacl release of the switch. At this time, however, sincethe regular release circuitis closed, and since release trunk conductor6 is not grounded otherwise, the eilect is entirely ditlerent; therelease magnet is not locked up to the release trunk conductor 6, butinstead the ground potential which is being supplied to the releasemagnet through armatures 3l and 33 is extended through the restingcontact and armature 27 of relay 2l and the working contact and armature38 to release trunk conductor 6 to maintain the selector D busy duringits releasing operation. lt will be noted that armature 38 disconnectsthe lower terminal of the switching relay 26 trom the release trunkconductor G at its resting contact so as to prevent an energization otrelay 26.

TNhen the switch reaches its normal position, oil normal contacts 535open the circuit of release magnet 36, whereupon release magnet 36 fallsback and disconnects release trunk conductor G trom ground and connectsit to relay 26 again. l

lt will be appreciated that ii' it were not for the provision oi' theabove explained arrangement lor preventing a possible seizure of' theselector D during its releasing operation, such a seizure might welloccur with the result that relays 22 and 23 mightbe energized by thetime the normal posit-ion ot' the switch is reached, which case relay 2loperates prematurely (and locks up) because its lower winding is placedin multiple with ott normal contacts 35 by armature 34 ot relay 23. The

might be made higherand in thatrcase be likelihood of this occurrence,however, is ob- ,viated in the manner above pointed out.

Regarding the utility of the resistance element 29, it may be pointedout that, in many cases, double wound relays arek available which havetheir low resistance windings placed upon the armature end ot' the coresand their lock-ing,` windings uponthe heel end of the cores. A relay ofthis type is usually wound so that the low resistance winding hassutlicient turns to produce a comparatively heavy pull when the winding`is inserted into the circuit in series with the release magnet. lt, hasbeen found by experiinentthat the flux generated by this low resistancewinding is suflicient to attract the armature ont the relay so quicklythatthe relay operates to close its locking circuitaiid toopen thecircuit ci its energizing winding with the portion et the core encircledby the locking winding practically unmagnetized and with the armaturebeing,` attracted only by the leakage flux which takes `a pathexcluding' the heel end of the core. Under such conditions, themagnetism in the armature end of the core dies away responsive tobreaking` of the circuit ot the low resistance winding and permitsthearmature of the relay to be retracted before the flux can be built upthrough the heel end of the core sufficiently to exert a holding`iniiuence upon `the armature. As a result, the lockingV circuit is againopened and the initial circuit is again closed and the relay merelybuzzes instead ot operating` `ullyand locking up as desired. u

ln orderto prevent the above occurrence, i

the low resistance winding` or' the relay may be made (in relaysconstructed esiiecially for operation in this circuit) of a smallernuinl bei t turns ot wire, so that the flux generated by this windingwhen it is connected in sei-ies wiih the release magnet ot the switchisnot :liuiiiricnt to operate the armature oil the relay until it haspermeated the entire core and heel piece. When the circuit of thelocking winding is `closed under these conditions, the this is alreadybuilt up, and it is vonly necessary Ytor the locking` wii'iding tomaintain the established'iiiii; in order to hold the armature in itsoperated position. Y

ln order to adapt relays for use in this circuit which have not beenwound especiallyv tor this'speciiic circuit,vit'is deemed best to shuntthe low resistance windingwith the low resistancer element 29 which cutsdown the current flow through the windingto such` an extent that therelay operates in the desired 1placed in series with thelower winding ofthe relay 2l, but, in this case, the releasemagnet Sifi'would probablynot remain energized in series with theliigh resistance necessaryvto thelower winding ot the relay tooperate as desired, and there would be alikelihood that the release magnet might fallback and open the circuitoi the lower winding of the relay before sufficient time is allow-ed torthe relay to operate and become locked up.

Vihat is claimed is:

l. In an automatic switch ot the drop-back type, circuit arrangementswhereby K `the switch normally restores to its nerim-l `position toabsorb a digit, except when a certain digit is called, and contactscontrolledin ac cordance with the extent of the movement of the switchwhen the saine is operated in accordance'witli such certain digitprevent such restoration of the switch tonornnil. i

2. ln a drop-back switcli, circuit arrange ments including contacts atwhichthe rotary magnet ,circuit is open and contacts at which therelease magnet circuit is closed atthe end oic the primary movement ofthe selector, said contacts .in the rotary magnet circuit being` closedduring the release ct the switch, and contacts fon the release magnetfor main- ,tainingl the rotary magnet circuit open until plying? groundto 'said conductor. yduring` Vthe releasing operation e, of the,`selector, and

contacts on said release/magnet ioij disconnecting the switchingv relayfromkthe said release trunk conductor. i, o A

il. In a `Vdrop-back 4switch of the type in which a relay has itswinding shunted around oil' normal contacts to efectthe energization ofthe relay when the :off normal contacts ti'stnaihcd winding` so to adaptthe relay tor operation asabovc set tOrth.

5. ln' an automatic switchhaviiig wipers,

means including' a rotary magnet for movingthe wipers from their normal`positiona re lease magnet for restoring' the wipersto their normalposition, a guarding` conductor 1for said switch, and contacts onsaidrelease maggnet for applyinga guarding potential to said guardingconductor and tor opening` the cireuitof said rotary magnet during thereleasin?)` operation.

' (i.V ln Vaftelephone systeiina selector switch,

and means `for operating the same, f said switch primary movementanddeenergized on the vin av primary movement andan automatic selectingsecondary movement a y' 'y slow actingrelay energized during the initialcut down the current flow suilicieiitly t'oradapt tor preventing theautomatic release of said switch and for starting the automaticselecting secondary movement.

7. In a telephone system, a selector switch and means for operating thesame, said switch having a primary movement and an automatic secondarymovement, a release magnet for said switch, circuit arrangements wherebya circuit for said release magnet is normally closed after an initialprimary movement of said switch to automatically release the same, larelay lor preventing the automatic release of said switch on asubsequent primary movement, contacts on said release magnet andcontacts on said relay, an energizing circuit for said release magnetincluding said relay contacts, a locking circuit for said release magnetincluding said relay contacts and said contacts on said releasemagnet,and an energizing circuit for said relay including the windings oit saidrelease magnet and relay in series.l

8. In a digit absorbing or drop back selectorhaving /rimary andsecondary movements, a release magnet, a change-over relay energizedduring the primary movement and deenergized on the completion thereof, acircuit or said magnet normally closed by the deenergization of saidrelay to cause said magnet to energize and automatically release theswitch, a second relay, contacts on said release magnet closed when saidmagnet is energized for closing a circuit to operate said second relay,and contacts controlled by said second relay Jfor altering the switchcircuits so that a subsequent primary movement will be Jfollowedautomatically by the secondary movement upon the subsequentdeenergization of said change-over relay.

9. In a telephone system, a selector switch for use in connectingcalling and called lines, groups of trunk lines, said switch havingdirective primary movement to select a group and automatic secondarymovement, to select an idle trunk line in the selected group, a steppingrela-yV for controlling the automatic secondary movement, a sufitchingrelay for electrically connecting said switch with said selected trunk,a circuit for said stepping relay controlled by said switching relayincluding contacts on said switching relay, an energizing circuit forsaid switching' relay'includ- `ing the winding and a Contact of saidstepping relay, the circuit of said switching relay adapted to be openedat said contact when the stepping relay is energized, and 'a'.shuntingcircuit for said switching relay including theA said contact in saidstepping relay.

l0. In a telephone system, a selector switch and means tor operating thesame, said switch having a primary movement and an automatic secondarymovement, a release magnet for said switch, a change-over relayenergized during the primary movement and deenergized on the completionthereof, contacts on said relay closed on its deenergization forenergizing said release magnet to automatially release the switch, aguarding conductor in said switch, contacts on said magnet for Vclosinga locking circuit for itself which is er"- tective until the switch isrestored, means whereby the switch may be rcoperated to set lup aconnection and can be released thereafter, and a circuit including thesaid contacts on said magnet tor placing a guarding potential on saidguarding conductor during the last mentioned releasing operation. i

il. In a telephone system, a selector switch having primary andsecondary movements, means including a rotary stepping circuit foroperating said switch to establish a connection, guarding conductor forsaid switch, a release magnet for said switch, means for placing aguarding potential on said guarding conductor, means in said switch'responsive to the removal of guarding potential Jr'rom said conductortor operating sai-d release magnet to release said switch, and contactson said release magnet for replacing` guarding potential onsaid'guarding conductor and tor disabling said rotary stepping circuitduring the release of said switch.

l2. In a telephone system, a selector switch, means for operating saidswitch to establish a connection, a release magnet operated to releasesaid switch once during the establishment of said connection and oncethereafter, a guarding conductor in said switch, contacts on saidrelease magnetfor closing a locking cir- 'uitlor itself upon its lirstoperation, means for opening said locking circuit, and means for placinga guarding potential on said guarding conductor during the lastoperation of said release magnet, said. last means including saidcontacts. n

13. In a telephone system, a selector switch, means tor operating saidswitch, a guarding conductor in said switch, a release magnet in saidswitch, means for operating said release magnet under dierent conditionsto release said switch, and contacts on said release magnet for closinga locking circuit for itself when the magnet is energized under onecondition land for placing a `guarding potential on the guardingconductor during the' release of said switch when the magnet isenergized under another condition.

lll. In an automatic switch oic the drop-back type having primary andsecondary movement-s, circuits normally closed after the primarymovementrtocause said switch to restore to normal position to absorb adigit, and contacts controlled in acordance withthe exswitch responsiveto a particularly primary 10 e movement.

in witness whereof, hereunto subscribe my name this 29th day of January, A. D.. 1925. n ARTHUR J. RAY.

In Witness whereof, I hereunto subscribe my 15 name this 29th day of January7 A. D. 1925.

RUDOLPH F. STEHLIK.

